Exemplary embodiments pertain to the art of electric machines, and more particularly monitoring current flow in winding sets for electric machine.
Electric motors, are commonly used to convert electrical power into mechanical power to operate various devices on an aircraft. For example, ‘more electric’ aircraft architectures increasingly employ growing numbers of alternating current (AC) electric motors to operate devices traditionally powered hydraulically. Using such electric motors can aid in reducing weight and simplifying the arrangement of the aircraft. Such AC electric motors typically employ three-phase windings, which are provided AC power by the aircraft electrical system, and may operate at high frequency in cooperation with a motor controller.
In some applications it can be desirable to employ two or more winding sets for each AC phase in the electric motor. The winding sets are generally connected in parallel with one another to reduce winding resistance and inductance to limit electrical losses and to improve operation of the electric motor at high frequencies. The parallel winding sets are typically fed by a common phase lead, which connects the parallel phase leads to the AC power bus source lead through a motor controller. Current flow through the winding sets is generally measured at the phase lead and provided to the motor controller for monitoring current flow through the winding sets for each phase of the motor.
Occasionally, one of the windings in the motor may degrade or fail. Such degradation or failure can result in the currents in the three phases of the electric motor becoming unbalanced. Generally an imbalance in phase currents is detected by the motor controller and can result in a motor controller trip to an offline condition and loss of operation of the electric motor. In some cases, with certain winding degradation or failure, the phase currents may remain sufficiently balanced for the motor controller to continue operating the motor at lower power levels without tripping the offline condition. This occurs because the undamaged phase leg of the parallel windings accepts additional current to compensate for the degraded or damaged parallel phase winding. Unfortunately, under such a condition the failure remains partially masked such that the motor controller may not detect the failure, causing the losses in the remaining parallel winding to be higher and thereby reducing the life of that portion of the motor.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved current sensing in electric motors.